1. Field of the Invention
The invention relates to a sheeting of multilayer antidrumming lining material.
In general, the purpose of such sheeting of multilayer antidrumming lining material is to deaden vibrating substrates, more particularly bottom plates and the metal sheets of the transmission and propeller-shaft tunnels of automobiles. That is, to reduce the oscillatory capability of these substrates or metal sheets to dampen these vibrations.
2. Description of the Prior Art
To accomplish the foregoing, the substrates or metal sheets of motor vehicles are covered with antidrumming films. These sheetings of antidrumming lining material preferably consist of films containing bitumen a few millimeters thick. However, they are normally designed not only to achieve the antidrumming of the metal sheets, but also to withstand a fabrication process in the car factory which is integrated into the enamel baking. For this purpose, the antidrumming films are first placed on the chassis plates; this applies especially to the propeller-shaft tunnel on which is laid a special cut of antidrumming film, just like a saddle on the back of a horse. The chassis is then run through a paint oven in which prevail temperatures of about 180.degree.. The average passage time is about 30 minutes. In this paint oven, the antidrumming film fuses onto the chassis plate. To this end, antidrumming films are employed which plasticize in the paint oven and adapt to the contours of the metal sheets, so that a sound-conducting connection is produced between the chassis plate and the antidrumming film.
Particularly the strongly curved propeller-shaft tunnel requires excellent melting capacity and flowability of the antidrumming films, so that the neighboring bottom parts, too, are covered by the antidrumming film. A number of technological problems arise which, particularly in the case of the propeller-shaft tunnel, are attributable to the fact that in the normal position its sides are vertical, with the result that film areas along the vertical sides of the propeller-shaft tunnel, after they have been put on loosely, are not actually in contact with the vertical sheet metal components and consequently, during plastification, cannot fuse thereonto but tend to flow away.
A further problem is that the piece of antidrumming film for a propeller-shaft tunnel must often have a free cutaway portion so as to provide space for an opening in the top side of the propeller-shaft tunnel for the transmission gear shift lever. Now, during plastification of the antidrumming film, it is frequently observed that the edge against the side portions of the propeller-shaft tunnel flaps away therefrom, or flips over and fuses in a disorderly manner with the metal sheet. If, on the other hand, an antidrumming film is chosen which does not plasticize sufficiently in the paint over so as not to flap away from the vertical walls of the propeller-shaft tunnel, then the antidrumming film does not fuse at all onto the heavily curved parts of the substrate of the metal sheet of the propeller-shaft tunnel, since it does not follow the curves thereof.
Another reason for failure is that the steeply projecting exterior portions of the antidrumming film fuse in the bottom area next to the propeller-shaft tunnel before the film sufficiently softens and plasticizes, and thus cannot adapt to the contour of the propeller-shaft tunnel. The film is thus tensioned, hanging to a certain extent freely from the upper part of the propeller-shaft tunnel to the bottom. Then, at the instant of plastification, the film cracks under the influence of gravity.